The Boulder Magnetometer provides one set of measurements of the Earth's geomagnetic field, used to provide details of the surrounding space environment.

The Boulder Magnetometer has been in operation since 1961, by the USGS, and has provided a complete set of the magnetic field components D, H and Z since then. SWPC makes use of the data in it's daily forecast operations. A document of the early history of the site is available (USGS).